This invention relates generally to the field of direction indicating compasses, and more particularly to an improved compass device for underwater guidance of divers and which is characterized by a particularly low or substantially insignificant magnetic signature.
Location and disposal of underwater explosive ordinance, such as magnetic influence mines, are at times accomplished by divers equipped with specially designed non-magnetic breathing apparatus. The search and location phases of such an operation have been hampered in the past by the lack of a suitable non-magnetic compass or guidance means that a diver could safely carry to provide directional reference in carrying out a search pattern or in following a vectored course. In this regard, it has been found desirable to provide the diver with a compass device that provides a course or steering correction indication rather than a numerical or dial readout of actual heading.
Existing compasses or guidance devices for divers have utilized magnetized needles or magnet carrying compass cards or have utilized electrically operated magnetic flux gate devices having ferrite cores, magnetic flux concentrator, or the like, all of which exhibit a magnetic signature that far exceeds the level of five gamma at 4.5 inches that is considered the limit for safe use in the vicinity of magnetically sensitive explosive ordnance devices.
The development in recent years of what are known as Hall effect solid state electronic devices has provided the compass or guidance device art with an additional means for sensing direction through the earth's magnetic field. Examples thereof are found in U.S. Pat. No. 3,952,420 to R. P. Benjamin et al. and in U.S. Pat. No. 4,030,204 to R. A. Edwards. The former discloses the use of Hall effect devices in combination with oscillator clocked binary logic to generate a direct digital readout that presents the heading in degrees in numerical form. The second patent discloses an automobile compass utilizing two Hall generators in mutually perpendicular planes in combination, in one embodiment, with digital logic to generate an eight segment light emitting diode display indicating heading in cardinal and semi-cardinal points. In another embodiment linear amplifier means are used to drive a phase meter type of moving needle display to indicate heading. Neither of these types of indicating displays have been found to be well suited for use by a swimmer/diver in guiding his movements in that they require more attention and concentration on the display than the diver can reasonably devote. The second patent further contemplates the use of magnetic deviation compensation means incorporating movable bar magnets. The use of either compensating magnets or indicators having magnetic frames or cores produces a significant magnetic signature that the compasses, while useful for their intended purposes, do not answer the needs of diver's likely to approach magnetic influence explosive ordnance devices.